[time-nuts] "Piezo Little Wonder" OCXO
James.P.Lux at jpl.nasa.gov
Fri May 30 14:41:06 EDT 2008
At 10:37 AM 5/30/2008, you wrote:
>I have two PIEZO 10.230 MHz crystal oscillators in the same style package as
>the 10811. But the oscillator in question is for 10.238 MHz.
interesting.. is the 8kHz a deliberate offset? Is the manual tuning
off to one end? Maybe they were using them in a scheme where instead
of I/Q they did offset IF sampling.
>----- Original Message -----
>From: "Jim Lux" <James.P.Lux at jpl.nasa.gov>
>To: "Discussion of precise time and frequency measurement"
><time-nuts at febo.com>
>Sent: Friday, May 30, 2008 12:47 PM
>Subject: Re: [time-nuts] "Piezo Little Wonder" OCXO
> > At 08:33 AM 5/30/2008, you wrote:
> >>Early GPS receivers used a 10.23 MHz time base.
> >>Probably related to 2^10-1.
> > yep.. the chip rate for the C/A code is 1.023 Megachips/second, the P
> > code is 10.23 Megachips/second, and the L1 frequency (1575.42) is
> > exactly 154 times the 10.23 MHz, the L2 is 120 times.
> > So you can see that having a 10.23 MHz oscillator is a handy thing in
> > a GPS receiver, especially if you can discipline it with the received
> > signal.
> > These days, one might choose a reference oscillator somewhat higher,
> > so that when you do your 1bit A/D of the signal, you get many
> > samples/chip, and so that the signal directly aliases to somewhere
> > convenient. A lot of receivers use a sampling clock such that you get
> > 1 bit I and Q samples at a convenient sample rate. 4*10.23 would
> > work nicely, eh? 40.92 MHz
> >>Some GPS manufacturers approached HP about making
> >>a 10811 on 10.23 MHz. There is a circuit modification
> >>for 10.23 MHz and some crystals were made (I
> >>have some somewhere). However, I don't believe
> >>any 10.23 MHz 10811's were sold. This unit was
> >>probably intended to meet the need not filled by HP.
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